1. Field of the Invention
This invention relates to a method and an apparatus for planarizing or flattening a surface of a work.
2. Description of the Related Art
In a one-side surface lapping apparatus, a block 110 having wafers attached thereto is pressed against a lower surface plate 300 while being held by a head 200 so that the surfaces of the wafers 100 are lapped or planarized by the lower surface plate 300 which is driven to rotate.
With such a one-side surface lapping apparatus, however, an urging force or pressure of the head 200 is not always applied to the wafers 100 in a uniform manner, but sometimes localized.
As a consequence, the lapping or planarizing rate of each wafer 100 is varied at respective portions of the surface thereof so that the surface of each wafer 100 may not be flattened or planarized to any satisfactory extent.
Thus, the technique of flattening or planarizing the surface of each wafer 100 is conventionally applied to a one-side surface lapping apparatus or the like.
FIGS. 11(a) through 11(c) are schematic cross sections showing a conventional wafer planarizing technique. This technique is to adjust the distribution of the urging force or pressure applied to each wafer 100 by use of a ring.
Specifically, as shown in FIG. 11(a), an annular ring 210 is attached to the lower surface of the head 200, and a block 110 is mounted on a lower side of the ring 210. Thus, the urging force applied to the block 110 is the greatest at the annular ring 210. Therefore, the distribution of the urging force applied to the wafer 100 can be made substantially uniform by adjusting or changing the diameter of the annular ring 210.
Speaking concretely, in the case where the radially inner portion of the wafer 100 is lapped or planarized more than the radially outer portion thereof by the use of a small-diameter annular ring 210, as shown in FIG. 11(a), another annular ring 210 having a larger diameter is prepared and used in place of the small-diameter ring. In this case, however, if the radially outer portion of the wafer 100 is lapped or planarized more than the radially inner portion thereof, as shown in FIG. 11(b), a further annular ring 210 having a diameter slightly smaller than that ring is prepared and installed. Such a trial-and-error process is repeated to find a just-fit ring of an exact diameter.
In this manner, if an annular ring 210 of such a size as to allow a substantially equal partial pressure to be applied to the entire surface of the wafer 100 is prepared and installed, the surface of the wafer 100 can be planarized or flattened in a uniform manner, as shown in FIG. 11(c).
However, the above-mentioned conventional technique has the following problems.
In order to make uniform the urging force applied to the wafer 100, it is necessary to prepare an annular ring 210 of a suitable diameter and mount it to the lower surface of the head 200 in such a manner that the center of the annular ring 210 is accurately in coincidence with the center of the lower surface of the head 200. It is lucky if such operations (i.e., preparation and mounting of such a ring) are required and finished only once or just few times, but in general it is necessary to actually attach many annular rings 210 of varying sizes to the head 200 and detach them therefrom repeatedly a number of times by the time when an appropriate annular ring 210 of a just-fit diameter is found, Thus, these troublesome operations have to be conducted repeatedly for a relatively long period of time. Moreover, once the annular ring 210 attached or adhered to the head 200 is detached or peeled off, it can not be reused.
Thus, the annular ring 210 elaborated with much trouble cannot be reused for the subsequent adjustment work, and become useless.